Process of cutting gears.



W. F. ZIMMERMANN. PROCESS OF CUTTING GEARS. APPLICATION IILED MAY 25.1907.

Patented Mar. 23, 1909.

ATTORNEY gears, may be explains WILLIAM'F. ZIMMERMANN, or NEWARK, NEWJERSEY.

PROCESS OF CUTTING GEARS.

Specification of Letters Patent.

Patented March 23, 1909.

Original application filed February 18, 1907, Serial No. 357,844.Divided and this application filed May 25, 1907. Serial No. 375,601.

To all whom it may concern:

Be it known that I, WILLIAM F. ZIMMER- MANN, a citizen of the UnitedStates, and a resident of the city of Newark, in the county of Essex andState of New Jersey, have invented certain new and useful Improvementsin the Process of Cutting Gears; and

I do hereby declare the following to be a full, clear, and exactdescription of my invention, such as will enable others skilled in theart to which it pertains to exercise and perform said process.

The present accepted theoretically correct method of cutting the teethof spiral and spur gears, results in producing gears which are notnoiseless. The cause of the humming noise observed in high fipeedintermeshing manner. When the teeth of wheels are congostructed inaccordance with the accepted theoretically correct method, so as toproduce absolutely continuous motion, it is found that when such gearsare rotated in mesh at a high speed, a humming noise is produced,because of the fact that v. hen the point of contact between twointermeshing teeth is substantially in the line of centers, the adjacentteeth are out of contact. As

the two contacting teeth advance, there is a.

sensible space of time when there is a single pair of teeth in contactand another sensible space of time when two pairs are in contact. Whenthe first pair recedes, and the second pair approaches, it leaves-thesecond pair in contact, thus throwing the entire load upon that pair,until the next pair approaches in contact, when the strains are a aindivided between the two pairs. T ese sudden changes of strains from fullload to half load, cause a series of shocks \ihich at high speed,produce the humming noise heretofore referred to. I have discovered thatby deviating slightly from the theoretically correct tooth, I am able tocompletely overcome this humming noise and produce silent running gears.In order to do this, I so shape the teeth that the load of the recedingpair of teeth is gradually diminished and simultaneously, the pressureupon the approaching pair is radually increased, so that there is no suden transition from full load to half load, and from half load to fullload, between any successive pairs of teeth, and by doing this, I findthat these series of shocks are completely elimiin the followingrecedingpair of teeth, and a radual increase of pressure upon the approac ingteeth, such degree of pressure ranging from maximum or full load, tominimum, or but an infinitesimal fraction of a load, the reduction ofload upon one pair taking place simultaneously with the increase of loadupon the approaching pair. The same result may be 0 tained by slightlyundercutting the bases of the teeth to a degree some: hat in excess ofthat dictated by the present accepted theory, u hile the points of theteeth may remain the same as prescribed by theory. The same re-" sultmay be obtained by both relieving the points of the teeth andundercutting the bases. In the latter case, however, the degree ofrelieving and undercutting amounts to a fair average of the tr. 0 formermethods; that is, the points are relieved to a degree a trifle less andthe undercutting to a degree a trifle less than uhere the relievingalone or the undercutting alone r. ould be adopted.

In the descriptive matter following, it Will be noted that I havedescribed the process in connection with hob cutters. It is obvious,however, that the process may be as readily carried out with the use ofa reciprocating cutter in which the cutter itself is given not only itsreciprocating motion, in aplane substantially parallel to the tangent ofthe helix of the cutter, and at the same time, giving said cutter alateral 'motion equal to the travel of the helix during its completerotation.

In describing my process, I will refer to the accompanying drawings, inwhich Figure 1 is a side view of a spur gear with animproved form of hobcutter shown in position for beginning the cutting of the teeth. Fig. 2is a similar view of a spiral gear. Fig. 3 is a sectional viewillustrating the improved cutter in connection with the teeth of a gearwheel in the act of carrying out my process. Fig. 4 illustrates the formof two consecutiw teeth com leted by my process, with the theoretical ycorrect shape of such teeth shown in dotted lines. Fig. 5 is a viewsimilar to Fig. 4, showing a greater degree of undercutting. Fig. 6illustrates the method-of carrying out my process, with a so-called 5rack tooth hob of shortened pitch. Fig. 7 illustrates another method ofcarrying out the process with the so-called hour glass hob. Y Fig. 8illustrates the sides of a pair of consecutive teeth with the pointsonly relieved. 10 Fig. 9 illustrates a pair of consecutive teeth withthe points relieved and the bases undercut.

In Fig. 1, I have shown an improved hob cutter, such as that illustratedin my appli- '15 cation for Letters Patent, filed February 18,

1907, Serial Number 357 ,844, particularly in Figs. 2 and 3, of whichsaid application, this is a division. In this particular case, the slotsin the face of the hob forming the cutting teethare arranged par allelto the axis of said hob in which case, it is only necessary in cuttingspur gears, to set such hob at an angle with the horizontal, or at anangle with the plane of the gear to be cut, equal to the angle of thehelix. In this particular style of hob, it will be noted that the sides1 are 'not straight as has hitherto been the custom of forming suchteeth, but they are curved to a degree diflering slightly from a reversein: volute. The curves of the face of the teeth, however, aresymmetrical with respect to the axis of the tooth, such axis beingillustrated by the dotted lines 2. tions of the finished tooth withrespect to I the hob, it will be noted that the pointsof the teeth arerelieved to a degree commensurate with the departure of the face of thetooth of the hob from the line which would be dictated by the acceptedcorrect theory. It will also be noted that the curvature of the face ofthe tooth near the point results in slightly undercutting the base ofthe tooth, as comparatively illustrated in Figs. 4 and 5, in each ofwhich cases, the dotted lines 3illustrate the face of theoretically cutin volute teeth, while the full lines illustrate the deviation,resulting from cutting teeth by my improved process.

As above set forth in the brief description, Fig. 3 is a sectional viewillustrating the improved cutter in connection with the teeth of a gearwheel in the act of carrying out my process. This figure may serve toillustrate two ways of carrying out the process; forexample, it mayrepresent the cross-section of a hob with shortened pitch and curvedteeth, or it may represent a hob with normal pitch and lengthened teeth,said teeth having curved faces. When the pitch of the hob is shortrened, and the points of the teeth correspondingly lengthened, it isunnecessary to set the hob to make more than the normal depth of cut'inthe blank and the resulting teeth will be found to be undercutsubstantially as illustrated in Fig. 5. With the hob of less oiaeaspitch, this undercutting and relieving of ppgits is fully taken care ofin the rocess.

en I speak of increasing the lengt of the teeth of the hob, I mean thatthe total diameter of the hob over the points of the teeth is increasedover what the theoretically correct diameter of a hob for similar workshould be The degree of the undercutting of the base of the tooth willdepend upon the sharpness of the curvature of the face of the cutternear its point, or what amounts'to the same thing, the width of the faceof the tooth of the cutter, and the degree to which the point of thetooth will be relieved, will depend upon the thickness of the base ofthe cutter tooth, which in all cases, should be only sufficient toproduce the desired result.

As above stated, the result may be obtained by the use of a hob cutterwith teeth having straight sides as illustrated in Fig. 6. In this case,however, the pitch 4 of the cutter is shorter than the normal pitch ofthe theoretically correct cutter, the degree of such shorteningdepending upon the amount or extent to which'it is desired to relievethe points of the teeth. In this case, the sides of the teeth of thecutter are symmetrical with respect to the axis of the teeth; while thediameter of the hob is increased over the normal, resulting in thelengthening of the teeth of such hob as above described,

l but with this structure, no undercutting is In the successive posi- 7made.

In Fig. 7, I have shown how my processmay be carried out by the use ofthe hourglass type of hob cutter. In this case, the

axes of the teeth are radially arranged and are of such a thickness attheir bases, as to produce the necessary relieving of the points of theteeth in the gear to be cut. The curve of the face of this cutter is amean-curve produced normally to the curved teeth ofthe two types ofcutters described in connection with Fig. 3; and the cutter illustratedin Fig. 6 represents the chord of this are or curve. a

The principles involved in the use of the several forms of cuttersdescribed, are analogous in that they are diflerent ways of producingsubstantially the same result, that is, the productionof noiselessgears, by either relieving the points of the teeth, or undercutting thebases thereof, or both relieving the points and undercutting the bases.These same results are obtained in the cutting of spiral gears asillustrated in Fig. 2,. where the cutter is shown in the act ofbeginning the cut of a spiral gear wheel, the axis of the cutter beinginclined to the horizontal, to a degree e ual to the angle of the helixof the teeth in t e spiral, plus the aiigle of the normal to the helixof the hob to its axis.

As previously set forth, I am able to produce the same results and carryout the same 13 process by the use of a reciprocating cutter, 1n whichcase, the reciprocating cutter travels in a path substantially parallelto the teeth of the gear to be cut, and at the same time, is given alateral feeding motion during the reciprocation of the tool, the limitsof such lateral motion being substantially the same as the limit oftravel of the helix from one end of the same to the other, in whichcase, Figs. 3, 6 and 7 might be used to illustrate the successivepositions of the cutter in its lateral movement, to give the requisiteundercutting and relieving of the bases and points of the teethrespectively.

I claim: I

1. A process for shaping gear teeth, which consists 1n operating a racktooth shaped tool successively upon each of the teeth in thegear blankbeing cut, rotating said blank and simultaneously advancing sa1d toolwith said rotation in a path substantially at rightangles to said teeth,said path being slightly shorter at each successive tooth than the pitchof said teeth to slightly alter the .contour of said teeth from thetheoretically correct contour, thereby completing the gear when the toolhas made one passage at right angles to the teeth.

2. A process for shaping gear teeth, which consists in operating a racktooth shaped tool on each of the teeth in the, gear blank being cut,rotating said blank and advancing said tool simultaneously with saidrotation in a path substantially at right-angles to said teeth, saidpath being slightly shorter than the pitch of said teeth to complete atooth of the gear by having the tool cut successively upon each of theteeth inthe gear.

3. A process for shapin gear teeth which consists of operating a he 'calor hob cutter, having rack shaped helices, the pitch of said helicesbeing. slightly shorter than the gear being cutsuccessively u on each ofthe teeth, rotating the ear b ank and simultaneously advancing t e saidhelices in a path substantiall at right angles w ith said teeth, saidpath eing slightly shorter than the pitch of said teeth, allsubstantially as and for the purpose specified.

4. A process for shaping gear teeth which consists of operating anangularly adjustable helical or hob cutter, having rack shaped helicesthe pitch of said helices being slightly shorter than the gear being cutsuccessively upon each of the teeth, feeding said helical cutter in apath substantially parallel with the face of the gear blank, rotatingthe gear blank and simultaneously advancing said helices in a pathsubstantially at ri ht angles to said teeth, said path being slightdyshorter than the pitch of said teeth to slightly alter the contour ofsaid teeth from the theoretically correct contour. I

5. A process for shaping gear teeth, which consists in operating a racktooth shaped 6. A process for shaping gear teeth which consists ofoperating a helical or hob cutter, having rack tooth shaped helicessuccessively upon each of the'teeth, said helices havm a correctedcutting contour, so

shape that the resulting path described by the cutting faces produces analteration in the contour of the gear teeth, rotating the gear blank andsimultaneously advancing the said helices in a path substantially atright angles with, said gear teeth, said path differinglfrom the path ofthe theoretically shaped he 'ces to slightly alter the contour of saidteeth from the theoretically. correct contour.

7. A process forshaping gear teeth w hich consists of operating anangularly adjustable helical or hob cutter, havin rack shaped helicessuccessively upon eac of the teeth, said heliceshavin a correctedcutting contour, so sha ed, that the resulting path described by t ecutting faces produces an alteration in the contour of the gear teeth,feeding said helical cutter in a path substantially parallel with theface of the gear blank, rotating said gear blank and simultaneouslyadvancing said helices in a path substantially at right angles with sa1dgear teeth,

. retically correct contour.

8. A process for shaping gear teeth which consists of'operating anangularly adjustable helical or hob 'cutter havin rack shaped helicessuccessively upon eac of the teeth, I

said helices corrected to pointto a common center, thereby altering thecontour of said teeth from the theoretically correct contour,

feeding said helical cutter in a path substantiallyparallel vi ith theface of the gear blank, rotating said gear blank and simultaneouslyadvancing said helices in a path substantially at right angles with saidgear teeth, said path differing from the path of the theoreticallycorrect shaped helices to slightly alter the contour of said teeth fromthe theoretically correct contour.

This specification signed and witnessed this 19th day of A ril 1907.

WILLIA F. ZIMMERMANN. Witnesses:

LOUIS M. SANDERS, FREDK O. FISCHER.

